// 泛型 generics
function dump(arg) {
    return arg;
}
var str = dump('string.....');
var bool = dump(true);
var num = dump(21); //它会自动能推断的类型
// extends
function getLength(arg) {
    return arg.length;
}
console.log(getLength('coderzrf'));
console.log(getLength([1, 2, 3]));
